The present state-of-the-art satellite paging systems comprise a fixed position antenna mounted on a satellite in synchronous orbit. Typically in such systems, the antenna and the beam pattern of the antenna are both fixed so that the spot or the "footprint" of the signal beam covers that portion of the globe which is "visible" to the satellite; that is, approximately one-third of the earth's surface.
The ground level strength of the signal transmitted by the antenna is fairly uniform across the covered area; however, the signal strength is very weak. This creates a problem, even for the highest powered synchronous satellites, since the ground level signal strength is too weak to allow for in-building paging coverage. For example, for a synchronous satellite with a radiated power of 400 watts, a state-of-the art selective call paging receiver using the POCSAG paging protocol at a bit rate of 512 bits per second would only have 2 dB of signalling margin; that is, the average signal strength on the ground would be only 2 dB above the minimum level to activate a paging device. One solution would be to use low bit rate signals of 60 baud or less to reduce the bandwidth of the paging receiver. However, this makes the paging system extremely expensive and impractical in view of the small number of users that can be serviced by the paging system. That is, the low bit rate could only support a small volume of paging traffic.
Thus, it is an object of the present invention to provide an improved satellite signalling system wherein the above disadvantages are overcome or at least alleviated.